The invention pertains to an optically anisotropic solution containing a mixture of a paraphenylene groups-containing, wholly aromatic polyamide component and another polyamide component in a suitable solvent such as concentrated sulphuric acid. The invention also pertains to fibers made up wholly or for the most part of a mixture of a para-aromatic polyamide component (p-aramid) and some other polyamide component, which are to be made by spinning the solution in a conventional manner.
Such solutions, and fibers made therefrom, are known from JP 57-183 420, which describes a spinning solution of a mixture comprising 55 to 95 wt. % of para-aromatic polyamide, and 5 to 45 wt. % of some other polyamide. A number of feasible para-aromatic polyamides are listed, as is a wide range of other polyamides. The embodiments concern fibers made from spinning solutions of polyparaphenylene terephthalamide (PPTA) and N-modified PPTA (N-carboxymethyl PPTA and N-propyl PPTA), i.e., both polyamides are p-aromatic polyamides.
Especially because of the adhesion of p-aramid to rubber it is desired that the aramid should be miscible with an aliphatic polyamide. This is known, e.g., from JP 59/116411, wherein a polyamide fiber is described which has a strong rubber adhesion, made up of 97-100 wt. % PPTA and 0-3 wt. % of an aliphatic polyamide. However, as is also apparent from the relatively low single filament strengths mentioned, it was found that the addition of an aliphatic polyamide to a PPTA spinning solution produces a dramatic deterioration of the mechanical properties of the resulting yarns. More in particular, yarns made from such a spinning solution were found to have low breaking strength, low loop strength, and low cord efficiency.
The invention has for its object to provide fibers, and notably multifilament yarns, with better adhesion to rubber than corresponding fibers and filament yarns of PPTA, but also with mechanical properties which are not actually inferior to those of PPTA and preferably at least comparable.
The prior art concerning mixtures of aromatic and aliphatic polyamide includes JP 57-115,452. From this document hot melt-formable polyamide compositions are known. The disclosed compositions comprise a hot melt-formable, aromatic group-containing polyamide and a wholly aromatic polyamide. It is noted that an aliphatic polyamide may be added thereto. In addition, the description makes mention of a solution of nylon-66 and PPTA in 98% sulphuric acid. This is not a spinning solution. The dissolving of the polyamides, with the polymer content in the solution being a mere 5%, serves to arrive at a properly mixed composition. To this end the sulphuric solution is poured into water, washed, and dried, followed by the mixture being hot melt-formed. From JP 57-115,452 melt-spun fibers are known which are made up of a mixture of meta-aramid and aliphatic polyamide.
Mixtures of aromatic and aliphatic polyamide are also known from GB 2,008,598. This publication does not pertain to fiber spinning, but to the preparation of a polymer composite material.
Additional background literature is constituted by the following publications. JP 118367/1988 teaches a resin composition comprising a polyamide resin composed of an aromatic polyamide and polyamide-6,6. From JP 59/163418 another fibrous product made from a spinning solution of PPTA and an aliphatic polyamide is known, viz. a fibrillated fiber that can be made into paper. Further, EP 392 558 teaches spinnable dopes containing a mixture of fiber-forming polymers, one of which, in 55-80%, being para-aramid, the other, 20-45%, being a thermally consolidatable polymer. Rather than pertaining to an anisotropic spinning solution such as is normally required for making industrial fibers of sufficient strength, the disclosure prescribes that the spinning solution be a two-phase solution comprising interdispersed anisotropic and isotropic phases.